1. Field of Invention
The invention relates to a fan and, in particular, to a centrifugal fan.
2. Related Art
In the conventional electrical system, the electrical component, such as a CPU, is usually provided. The electrical component generates heat and may have lower performance at the high temperature. In such a case, to maintain the acceptable performance of the electrical component, the generated heat must be removed as soon as fast. To achieve this objective, a blower is usually adopted to dissipate heat quickly.
In the present, there are two most popular fans including the axial fan and the centrifugal fan (or the blower). Since the centrifugal fan provides airflow with higher pressure, it can achieve better heat dissipating effect. Thus, the centrifugal fan has become the major trend. As shown in FIG. 1, the conventional centrifugal fan 1 includes a casing 11, an impeller structure 13 and a driving device 15. The casing 11 has an axial inlet and an outlet 111, and the impeller structure 13 and driving device 15 are installed inside the casing 11. The blade set 131 of the impeller structure 13 is located corresponding to the outlet 111. In this case, when the driving device 15 drives the impeller structure 13 to rotate, the blade set 131 presses the air to generate the airflow through the outlet 111.
However, the centrifugal fan 1 can only provide a one stage compressing, so the pressure increasing effect of the centrifugal fan 1 is limited.
It is therefore an important subject of the invention to provide a centrifugal fan that can enhance the pressure increasing effect.